A movable contact unit for panel switch of the prior art is described hereinafter by referring to a cross sectional side view of FIG. 7A, an exploded perspective view of FIG. 7B, a cross sectional side view of FIG. 8, and a fragmentary cross sectional view of FIG. 9. A dome-like movable contact 1 constructed of a thin resilient sheet metal is placed in each of a plurality of openings 2B provided in a sheet 2 formed of an insulation film coated with adhesive material 2A on its underside surface. The movable contact 1 is adhesively conjoined of its upper surface, and fixed in its position by a dustproof sheet 3 of a flexible insulation film in a size slightly greater than the opening 2B glued over the openings 2B of the sheet 2. Then, a flexible conductive sheet 4 is adhered from the above to constitute the movable contact unit 20 for panel switch.
In the movable contact unit 20 for panel switch having the above-described structure, a release liner 5 is adhered on an underside of the sheet 2 by the adhesive material 2A on the underside of the sheet 2 to cover the openings 2B, in order to prevent dust from entering into the openings 2B of the sheet 2, and to avoid it from sticking to the other movable contact unit 20 while in the transportation and/or storage. When the movable contact unit 20 for panel switch is assembled into an electronic equipment, the release liner 5 adhered on the underside of the sheet 2 is removed first, and the movable contact unit 20 is adhered with the adhesive material 2A on the underside of the sheet 2 by overlaying it on a substrate circuit board 8 having a plural pair of electrically independent stationary contacts 6 and 7 located in positions corresponding to an outer periphery 1A and a top center area 1B of the individual dome-like movable contact 1. A panel switch 21 depicted in the cross sectional side view of FIG. 8 is thus completed, when an actuating board 10 made of an elastic rubber or the like material and formed integrally with an actuating button 9 for depressing each of the dome-like movable contact 1 is mounted.
The conductive sheet 4 on the top surface of the movable contact unit 20 of the panel switch is provided for the purposes of suppressing an extraneous emission of electromagnetic waves from actuating portions of the electronic equipment mounted with the movable contact unit 20, and for draining static electricity, which flows into the movable contact unit 20 from the actuating button 9, to a conductive part for grounding. For this reason, the movable contact unit 20 of the panel switch is usually adhered on the substrate circuit board 8 with an edge of the movable contact unit 20 folded back in a manner to make the conductive sheet 4 electrically in contact with a grounding circuit part 11 deposited on the substrate circuit board 8, as shown in the fragmentary cross sectional view of FIG. 9.
Referring now to FIG. 8, the panel switch 21 operates in a manner as described hereinafter. When the actuating button 9 is depressed, the pressure is transmitted to the dome-like movable contact 1 positioned over the stationary contact 6 via a projection 9A of the actuating button 9, the conductive sheet 4 and the dustproof sheet 3. If the pressure exceeds a predetermined force, the dome-like movable contact 1 is flipped with a tactile response, and the top center portion 1B touches to the stationary contact 7 on the substrate circuit board 8, thereby making an electrical connection between the stationary contacts 6 and 7 through the dome-like movable contact 1. When the depressing force is removed from the actuating button 9, the dome-like movable contact 1 is flipped back to its original shape by its own resiliency to open electrically between the stationary contacts 6 and 7.
As described in the foregoing, the movable contact unit 20 for panel switch and the panel switch 21 using the same have the structure, wherein an upper side of the dome-like movable contact 1 is overlaid with two layers of sheets, i.e. the conductive sheet 4 for a countermeasure against the extraneous emission of electromagnetic waves and the static electricity, and the dustproof sheet 3. Due to this structure, a discernible feel of actuation, or a tactile response, of the dome-like movable contact 1 is somewhat reduced, since the depressing force and the resiliency of the dome-like movable contact 1 are absorbed by the conductive sheet 4 and the dustproof sheet 3. Although a thickness of the two layers needs to be reduced in order to improve the feel of actuation, there has been a problem that it requires a high level of adhering technique and expensive assembling apparatuses in manufacturing the dome-like movable contacts 1, since the thinner they are the more difficult they become to handle.
The present invention is intended to improve the above problem, and it aims at providing a movable contact unit for panel switch and a panel switch using the same that suppresses an extraneous emission of electromagnetic waves and reduces an adverse effect of static electricity, yet gives an excellent feel of actuation.